1. Technical Field of the Invention
The present invention relates to vehicle alternators and, more particularly, to a vehicle alternator having a protector cover structure.
2. Description of the Related Art
With vehicle alternators of the related art, it has been a usual practice for the vehicle alternator to include a protector cover, made of resin, which is fixedly mounted on a rear frame so as to cover a rear end face thereof for protecting a rectifier unit and a brush unit disposed on the vehicle alternator on one end face (hereinafter referred to as a rear end face) thereof in opposition to a drive pulley as disclosed in U. U. Patent No. 6294856 and Japanese Patent Application Publication No. 200-32720.
The rectifier unit of the vehicle alternator is disposed in a layout as simply described below.
With the vehicle alternator of the related art, the rectifier unit includes positive-side and negative-side heat radiator plates (hereinafter referred to as “positive-side and negative-side cooling fins”), which are axially spaced from each other by a given distance in face-to-face relation to the rear end face of the frame. Upper arm-side diodes are mounted on the positive-side cooling fin in a face-to-face relationship with each other and lower arm-side diodes are mounted on the negative-side cooling fin in a face-to-face relationship with each other. With the frame connected to the ground, it is normal practice for the negative-side cooling fin to be placed in a position near the rear end face of the frame and the positive-side cooling fin to be mounted on the resin-molded end cover that covers the rectifier unit. However, such a layout is not essential. The negative-side cooling fin is normally fixed to the rear end face of the rear frame with the same voltage potential. In an alternative, an attempt has heretofore been made to mount the lower arm-side diodes on the rear end face of the frame.
Each diode includes a bottomed cylindrical electrode terminal, a diode element having a bottom-side electrode surface fixed to the bottomed cylindrical electrode terminal, and a lead electrode terminal (hereinafter also referred to as a “diode lead”) fixed to an upper electrode surface of the diode element and protruding along a central axis of the bottomed cylindrical electrode on an open side thereof with resin being charged to a desired area for insulating protection in a unitized fashion.
The positive-side and negative-side cooling fins are formed of substantially horseshoe-shaped (substantially “U-shaped plate”) conductive metallic plates with opened ends thereof accommodating the brush unit and a voltage regulator. That is, the positive-side and negative-side cooling fins are designed to have a contoured space (also referred to as an “electric component-part compartment”) as wide as possible in an area, axially overlapping the other electric component parts, on which no other electric component parts are present. This is because such a layout increases heat radiating surface areas of the positive-side and negative-side cooling fins to minimize the temperatures of the diode elements acting as power semiconductor elements
Due to the increased heat radiating surface areas being needed, it has been a normal practice for the positive-side cooling fin to overlap the lower arm-side diodes fixed to the negative-side cooling fin as viewed in an axial direction. However, if the positive-side cooling fin radially overlaps the negative-side cooling fin to a great extent in excess, it becomes more likely that a short-circuited state occurs between the diode lead of the lower arm-side diode, protruding toward the positive-side cooling fin, and the positive-side cooling fin. Therefore, a need arises for ensuring a radial clearance between a circumferential edge portion of the positive-side cooling fin and the diode lead of the lower arm-side diode. To address such an issue, it has been known to have a structure wherein a partition wall portion is formed protruding from the plastic cover for electrical insulation in an area between the circumferential edge portion of the positive-side cooling fin and the diode lead of the lower arm-side diode.
Further, it has been a normal practice for the rectifier unit to include a terminal block intervening between the positive-side and negative-side cooling fins. The terminal block is comprised of a plastic plate embedded with A.C. conductive segments of various phases with the A.C. conductive segments of each phase interconnecting the diode leads and the stator leads in each phase.